Platform Builder/debugger extension: ReadMemory crashes the extension

I am trying to develop a debugger extension for my driver but I have
got an error when I launch one of the simplest testcase.

When I launch the "hello" command of my extension, I have got this
error window :

"Debug Error !
Program : ...
Module : ...\hello_ext.dll
File : c:\......\hello.cpp
Line : 42
The value of ESP was not properly saved across a function call. This
is usually a result of calling a function declared with one calling
convention with a function pointer declared with a different calling

Source of the failing entry point :
ULONG ulTest = 0;
ULONG ulBytesRead = 0;
ReadMemory(0,&ulTest,sizeof(ULONG),&ulBytesRead); //(line 42)

I have followed this Howto : How to Create and Debug a Debugger

"hello" is my only command
I am using PB WinCE 6.0 R2

Best Regards,